What is the cornea?
The cornea is the outermost fibrous coat of the eye. It is transparent, and made up of 4 separate layers: an outer epithelium, corneal stroma (which makes up 90% of corneal thickness), Descemet’s membrane, and corneal endothelium (the deepest layer).
The cornea protects the eye by providing a protective barrier resistant to bacterial colonization. Ulceration of the cornea is a common affliction of the eye that can lead to blindness if left untreated.
What is a corneal ulcer (Ulcerative keratitis)?
Corneal ulcers occur when there is damage to or erosion of any of the layers of the cornea. Ulcers can be classified as superficial or deep. Superficial ulcers involve the surface epithelium and possibly the superficial stroma. Deep ulcers extend through a greater part of the stroma and sometimes down to Descemet’s membrane.
Deep ulcers are particularly dangerous because they are progressively destructive and can lead to the eventual rupture of the eye.
What causes corneal ulceration?
There are many different ways that the cornea can become ulcerated:
1. Direct mechanical damage of the eye (the ulcer occurs at the site of the trauma)
• Trauma – caused by a scratch, abrasion, rubbing with a paw, perforation
• Abnormal hair contact – due to entropion (folding in of the eyelid irritates the surface of the eye), ectopic cilia (misplaced eyelashes on the inside of the eyelid)
• Foreign bodies (e.g. dirt, twigs, thorn, etc.)
• Eyelid tumors (an uncommon cause of ulceration)
2. Unhealthy surface environment
• Dry eye (keratoconjunctivitis sicca/KCS) – the deficiency of tears causes drying and inflammation of the cornea
• Exposure – if the cornea does not have an adequately distributed tear film, it becomes dry and devitalized, leading to ulceration. Exposure can be caused by facial paralysis that reduces the ability to blink, bulging eyes, or removal of the third eyelid
• primary corneal infection is more common in cats (caused by feline herpesvirus)
4. Corneal disease
• epithelial basement membrane disease
• endothelial dystrophy,
5. Breed predilections
• Boxers are prone to recurring ulcers known as “indolent ulcers”
What are the symptoms of a corneal ulcer?
Corneal ulceration is a very painful condition. Animals with corneal ulcers will show very obvious signs of discomfort:
• Increased tear production
• Squinting (called blepharospasm)
• Rubbing at the eyes
• Redness of the eye and eyelids
• Corneal edema (swelling of the cornea that gives it a cloudy or hazy appearance)
• Prolapse of the third eyelid
• Cats that have an ulcer caused by infection with herpesvirus may have an accompanying respiratory illness
If you suspect that your pet has a corneal ulcer, do not hesitate to call the veterinarian. Ulcers can progressively worsen, causing permanent damage if they are not promptly treated.
How does a veterinarian diagnose a corneal ulcer?
Diagnosis of an ulcer is very straightforward. Initially, most vets will place a topical anesthetic in the eye to allow for a thorough ocular exam. The vet will then place fluorescein dye in the eye. Fluorescein adheres to exposed stroma, defining the extent, and to some degree, the depth of the ulcer.
Some vets may perform an additional test before applying the fluorescein dye to the dye. The Schirmer tear test measures tear production and is useful for the diagnosis of dry eye. Once the vet has established the size and severity of the ulcer, he or she can recommend an appropriate treatment regime.
What are the treatment options for pets with corneal ulcers?
The management of a corneal ulcer depends on treating the underlying cause of the ulcer, and will vary according to the size, depth, and character of the ulcer. There are a range of treatment options for every kind of ulcer. However, there is one medication that should NEVER be used on an ulcer: steroids.
Treatment is generally a supportive measure to allow normal healing of the eye to occur. The cornea heals by migration of adjacent epithelial cells to cover the defect.
1. Superficial ulcers
• Topical antibiotics – controls infection
• Atropine ointment or solution – dilates the pupil and counteracts pain and muscle spasm
• Antiviral agents are occasionally used for cats with herpesvirus infections
• Elizabethan collar – prevents the patient from rubbing the eye and exacerbating the condition
• Revisits are essential to ensure that the ulcer has fully healed
2. Indolent ulcers – have loose flaps of epithelium that do no adhere to underlying stroma. Treatment is similar to that of a superficial ulcer, but also involves removing the loose epithelium so proper healing can occur.
There are a variety of such treatments:
• Topical anesthetic is applied to the eye and then a swab is rubbed around the edge of the ulcer to free the loose epithelium
• Phenol cautery – a swab dipped in phenol is used to cauterize the ulcer and healing usually occurs within a few days
• Superficial grid/punctuate keratotomy – with the eye anaesthetized, a needle is used to make a crosshatch pattern or spots on the cornea; thus speeding up healing of the cornea
3. Deep ulcers – these ulcers are far more difficult to treat than superficial or indolent ulcers
• Topical antibiotics
• Oral painkillers (e.g. aspirin)
• Anticollagenases – prevents progression of corneal destruction
• Elizabethan collar
• Contact lens – reduce irritation and pain sensation
• Deep ulcers may warrant veterinary check-ups every 1-2 days
Owners should monitor the progress of their pet’s therapy. Ensure that your pet is not rubbing its eye or doing anything that could further traumatize its eye. Check the eye regularly for signs of worsening of the condition (e.g. ocular discharge, cloudiness of the eye, continued squinting, inflammation, etc.). If you think your pet’s eye is getting worse instead of improving, contact your vet immediately.
What is the prognosis for a corneal ulcer?
The prognosis is very good for uncomplicated superficial ulcers. With appropriate treatment superficial ulcers usually heal in about 5-7 days. Because of the refractory nature of indolent ulcers, they make take weeks, or even months, to properly heal.
Deep ulcers will take weeks to months to heal, and require both intensive treatment and a dedicated owner. Even after deep ulcers heal, there may be permanent scarring of the cornea. Ulcers that go untreated, or are mismanaged, can lead to blindness.